Nonadiabatic Spin Transfer Torque in High Anisotropy Magnetic Nanowires with Narrow Domain Walls

Abstract

Current induced domain wall (DW) depinning of a narrow DW in out of plane magnetized ðPt=CoÞ 3 =Pt multilayer elements is studied by magnetotransport. We find that for conventional measurements Joule heating effects conceal the real spin torque efficiency and so we use a measurement scheme at a constant sample temperature to unambiguously extract the spin torque contribution. From the variation of the depinning magnetic field with the current pulse amplitude we directly deduce the large nonadiabaticity factor in this material and we find that its amplitude is consistent with a momentum transfer mechanism. DOI: 10.1103/PhysRevLett.101.216601 PACS numbers: 72.25.Ba, 75.60.Ch, 75.75.+a The recent discovery that a spin-polarized current can displace a domain wall (DW) through the spin transfer from conduction electrons to the local magnetization [1] has opened up an alternative approach to manipulate magnetization. Current induced domain wall motion (CIDM) has been investigated experimentally so far in detail in permalloy (Py; Ni 80 Fe 20 ) nanowires characterized by wide DWs (>100 nm) where the spin of a conduction electron is expected to follow adiabatically the magnetization direction as the electron passes across the DW [1,2]. A key question that has been raised is whether the spin transfer effect contains nonadiabatic contributions due to spin relaxation or nonadiabatic transport [2][3][4][5][6]. It was predicted [3,7] that from the efficiency of the spin transfer effect, which is measured by probing the dependence of the DW propagation magnetic field on the injected current, the nonadiabaticity can be deduced. However, in Py nanowires, the complicated 2D spin structures of the DWs prevent direct comparison to 1D models and a meaningful comparison to full 2D micromagnetic simulations is only possible if the exact spin structure during pulse injection is known, which is generally not the case. In particular, the wall deformations and transformations that have been observed [8] can render the results impossible to interpret in terms of the nonadiabaticity.To obtain simple DW spin structures, out-of-plane magnetized materials with a strong uniaxial anisotropy can be used where the simple Bloch or Néel DW spin structure is more apt for an analysis using an analytical 1D model including the nonadiabatic torque terms. In addition, a larger nonadiabaticity is expected in these materials due to the larger magnetization gradient for such narrow DWs [2,4,9]. This larger nonadiabaticity may explain the high efficiency of the current induced DW depinning reported recently in such materials [10,11]. However, another major obstacle for the determination of the nonadiabaticity from the dependence of the DW depinning magnetic field on current is that Joule heating strongly affects the thermally activated DW depinning. For experiments carried out at a constant cryostat temperature, it is thus hard to extract directly the contribution from the spin transfer torque.In this Letter we probe CIDM in out-of-plane magnetized ðPt=C...

Thermally assisted current-induced magnetization reversal in SrRuO3

“…The interaction of spin polarized current with magnetization gives rise to various fascinating spin-torque effects such as magnetization reversal of nanomagnets in junction configurations [1][2][3][4][5] and current-induced domain wall motion [6][7][8][9][10][11]. The interest in these effects is not only theoretically motivated, but also for their expected central role in novel spintronics devices, as they offer efficient and scalable methods to control magnetic configurations on a nanometer scale.…”

Current-induced domain wall motion in Co/Pt nanowires: Separating spin torque and Oersted-field effects

“…͓doi:10.1063/1.3405712͔ Current induced domain wall motion ͑CIDM͒ in ferromagnetic nanoscale wires holds promises for applications in the field of data storage or logic devices 1,2 and was observed by a number of groups. [3][4][5][6][7] Recent studies on materials with perpendicular anisotropy have revealed a higher efficiency for CIDM than in the case of in-plane magnetized materials. [8][9][10][11] Especially the contributions of the adiabatic 12,13 and nonadiabatic spin torque due to spin relaxation [14][15][16] or momentum transfer 12,14 to the domain wall ͑DW͒ motion and their dependence on the material properties are so far not fully understood.…”

Current-driven magnetic domain wall motion and its real-time detection

“…At the time, most of the CIDWM results were assumed to be predominantly governed by the non-adiabatic STT because the current densities required to move the DW were much smaller than the threshold value predicted theoretically on the basis of intrinsic pinning. This raised a question on the strength of the non-adiabatic STT, but a clear consensus was not reached because of large scattering of the values of the reported non-adiabatic STT parameter β, [24][25][26][27][28][29][30] which probably originated from the complex internal DW structures. The precessional behavior of DW motion 31,32) as well as the acceleration=deceleration of DWs [33][34][35] was also presented.…”